Can any one tell me why there were no G4000 units made in the G series? I thought I saw an ad in the early 80's with a pic of the G3000 and the G4000 side by side. After searching I can find no info on the G4000. I found info on the G401. Is the G401 a replacement for the G4000? Can anyone fill me in on this ? Thanx in advance.